A sensor element that has a function for modulating a detection of electrons generated by light inside a pixel, such as “an apparatus for detecting and demodulating an irradiation field whose magnitude is modulated, in a time domain, (see patent document 1)” announced in 1994 or the like is also referred to as a “lock-in pixel”
For example, a three-dimensional imaging system in which a pixel of a light detection detector, a dedicated electronic circuit and a corresponding processor are formed on a common semiconductor substrate by using a CMOS manufacturing technique is proposed (see patent document 2). In an embodiment of the patent document 2, each detector uses a time of flight (TOF) in which an optical pulse emitted by the system is reflected from a point on a physical body and focused and detected by a pixel detector and has a corresponding high speed counter for accumulating a clock pulse number proportional to a TOF data. The TOF data gives a direct digital scale with regard to a distance until the point on the physical body from which the emitted optical pulse is reflected. In another embodiment of the patent document 2, instead of the counter and a high speed clock circuit, a charge accumulator and an electronic shutter (S1) are placed in each pixel detector. Each pixel detector stores charges, and its total amount gives the direct scale of the reciprocating TOF.